Systems for administering liquids to a patient are widely used in clinical settings. All of these systems comprise a container for the liquid and a flow set for delivering the liquid to the patient. In general, the liquid is either allowed to drain through the flow set to the patient under the action of gravity or is pumped through the flow set. Systems using pressure sleeves on the container are also used. Systems using a pump are referred to in this specification as "pump systems".
In many instances, two liquids need to be sequentially administered to the patient. For example, it is often necessary when administering a feeding liquid to periodically flush the system with a flushing liquid to avoid blockages caused by the relatively viscous feeding liquid. Also, it is sometimes necessary to alternatively administer a saline solution and a liquid containing an active agent. In these cases, the system is connected to two containers; each container containing a separate liquid. The system must then switch from one container to the other as needed.
While it is possible to manually switch between the two containers, automatic switching is preferred. Automatic switching may be achieved, for example, by means of a valve actuator unit, such as that disclosed in U.S. Pat. No. 5,584,671, It also possible to separately pump liquid from the two containers using two pumps, each connected to a separate container and each being operated at a different time.
However, there is still a need for a system of sequentially administering two fluids to a patient which is safe, relatively simple, easy to use, and requires only one pump.